JPH0222907A - Automatic output controller - Google Patents

Abstract

PURPOSE:To prevent overshoot of the output power beyond a prescribed value at the time of setting a reference voltage by inputting the reference voltage to a comparator through a time constant circuit which compensates the time response characteristic of the output power. CONSTITUTION:A time constant circuit 9 which compensates the time response characteristic of the output is constituted, and a reference voltage VR is connected to the input point of this circuit 9, and the output point of the circuit 9 is connected to the reference voltage input terminal of a comparing circuit 4. Consequently, the time response characteristic of an output power PO to the reference voltage VR is a simple integral characteristic. Thus, the simple time constant circuit 9 is only added to obtain an automatic output controller where overshoot of the output power PO beyond the prescribed value is prevented even at the time of step-functional change of the reference voltage VR.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an automatic output control device, and particularly to automatic output control of a radio frequency power amplifier.

[Prior Art] A conventional automatic output control device for a radio frequency power amplifier is shown in FIG. FIG. 3 is a block diagram showing a conventional device, in which (1) is a preamplifier;
2) is a power amplifier, (3) is a detection rectifier circuit, (4) is a comparator, (5) is a DC amplifier, (6) is an input terminal, (7)
is the output terminal. Also, the input power of input terminal (6) is P
l, the output power of the output terminal (7) is Po, the output voltage of the detection rectifier circuit (3) is vI, the reference voltage input to the comparator (4) is ■R5, the output of the comparator (4) is ■. , the output of the DC amplifier (5) is represented by vo.

Preamplifier (1) by output VC of DC amplifier (5)
The output power P0 is feedback-controlled so as to be kept at a constant value determined by the reference voltage. That is, a comparator (4), a DC amplifier (5), a preamplifier (1
), a power amplifier (2), and a detection rectifier circuit (3) constitute a feedback loop, and are controlled so that V, =V.

Of this feedback loose loop gain, the DC amplifier (5), preamplifier (1), power amplifier (2),
The gains of the detection rectifier circuit (3) are expressed as G, , G, and G, respectively.
, G2. Let's call it G3. The gain G1 of the preamplifier (1) is ■
. For a unit increment of , the output of the preamplifier (1) is 01
・P means to increase by an amount.

Figure 4 is a connection diagram showing the internal connections of comparator (4) in Figure 3, where the same symbols as in Figure 3 indicate the same parts, (10) is the operational amplifier, and R1+R2 is the resistance value of each resistor. , C indicates the capacitance of each capacitor, and v+! is an operational amplifier (10
), and if the input impedance and amplification degree of the operational amplifier (10) are sufficiently large, then VR+ (VRVl) (R2+17SC)/R1=■
It becomes E. Note that S is an operator. This formula is τ1 ”
If you rewrite it as CR1+ τ, =CR, ■True(1+
s (τ1+τ2)) VI(1+sτ2)=sz−
IVt, and between ■E and vo nihaV, (1+sτ2
) = ■ Since there is a relationship, Fl (s) = (1+s
(τ1+τa))/Sτ.

If F2 (s) - (2 for 1+s)/45ft, -V,/sτ1 . . . (1) is obtained.

What is shown in equation (1) is the response characteristic of the comparator (4), and since VR is kept constant during operation, when 20 changes due to disturbance and VI changes, ■. The characteristic of Equation 0 (1), which has a response characteristic such that Po changes and returns to its original value, is the characteristic of a low-pass filter, but the detection rectifier circuit (3), comparator (4), and DC amplifier (5
) In order to prevent automatic oscillation and improve power supply ripple characteristics, such a low-pass filter circuit is usually inserted into the feedback circuit composed of the following.

The overall response characteristic is Po(s)=GsF2(S)・(1+Sf1/A
GS )・(2).

However, A=P, -G, ·G2 ·G4, and in equation (2), Po (S) and VR (S) are functions of S.

[Problem to be solved by the invention] In the conventional device as described above, when VR is constant, fluctuations in Po due to disturbance can be stabilized, but when vR changes like a step function, equation (2) ), there is a problem in that transient phenomena occur.

■Good changes when setting a given value for the first time.
When changing from one set value to another, the change is like a step function, and the largest number of steps is when setting a specified maximum value from a state of O. In this case, formula (2)% formula% ): If formula (3) is inversely transformed by Laplace, Po(t)・G,= (1+R1/R2)・Exp (AGs t/
τt)・(4), where t is time and Exp O
Since 0 normally τ2〉 representing an exponential function is 1, the response characteristics are mainly determined by τ2.

FIG. 5 is a characteristic diagram showing the characteristic expressed by equation (4), where the horizontal axis represents time t, and the vertical axis represents P, (t)·G,=V.

As is clear from equation (3) and FIG. 5, in the conventional device, the output power overshoots beyond the specified value when setting the reference voltage VR. This means the passing power of the power amplifier (2), and this passing power also means the excessive input from the power supply circuit (not shown) to the power amplifier (2), and these passing powers or excessive inputs may cause , there was a risk of deteriorating or destroying elements in the circuit.

Note that in the case of a radio frequency power amplifier, the transmission power may cause interference with other communications.

The present invention has been made to solve the above-mentioned problems, and an object of the present invention is to provide an automatic output control device that does not exceed a specified output when setting a reference voltage.

[Means for Solving the Problems] In the present invention, the output power P is expressed by equation (2). The reference voltage VR is input to the comparator (4) via a time constant circuit that compensates for the time response characteristics of the comparator (4).

[Operation] The time response characteristic of the output power Po with respect to the reference voltage ■λ becomes a simple integral characteristic, and even if ■8 is added like a step function, no overshoot occurs in the output power Po.

[Examples] Examples of the present invention will be described below with reference to the drawings. 1st
The figure is a block diagram showing an embodiment of the present invention. In the figure, the same reference numerals as in FIG. 3 indicate the same or corresponding parts.
) is a time constant circuit, R1 and R2 are the resistance values of each resistor, and C is the capacitance of the capacitor.

The transfer function G(s) of the time constant circuit (9) is = (1+
sτz>/(1+s(τ1+τ2)) = v in equation (2)
Substituting G(S) and vR(S) into R(S), the formula (2
) becomes (6), and if VR(S) = 1/S, then (7)
Then, if we perform Laplace inverse transformation, we get (-AG, t/τ1
)) ...(8).

FIG. 2 is a characteristic diagram showing the characteristics of formula (8), and is
The value approaches the specified value exponentially, and overshoot does not occur.

Furthermore, since AG3/τ1)1/τ2, the characteristic of equation (8) is shorter in time for the output to converge to the specified value than the characteristic of equation (4), and the response characteristic is improved. Furthermore, the expression (
Since the time constant τ2 is not related to the characteristics of 8), τ2 can be freely selected without considering the feedback loose characteristics. A relatively large τ
2 can be set freely, which means an increase in the degree of freedom in design.

In the above embodiment, the comparator (4) of the feedback circuit is
) is configured as shown in Figure 4, and we have shown an example of configuring the time constant circuit (9) that compensates for the time response characteristics of the output power. However, it is possible to construct a time constant circuit that compensates for the time response characteristics of output power.

Further, in the above embodiment, an automatic output control device for a radio frequency power amplifier has been described, but the present invention can also be applied to an automatic output control device for a general power amplifier.

[Effects of the Invention] As described above, according to the present invention, by simply adding a simple time constant circuit, even when the reference voltage changes in a step function manner, the output can exceed the specified value and overshoot. You can get an automatic output control device without.

[BRIEF DESCRIPTION OF THE DRAWINGS] FIG. 1 is a block diagram showing an embodiment of the present invention, FIG. 2 is a characteristic diagram showing the circuit response characteristics of FIG. 1, and FIG. 3 is a block diagram showing a conventional device. 4 is a connection diagram showing the configuration of the comparator shown in FIG. 3, and FIG. 5 is a characteristic diagram showing the response characteristics of the circuit shown in FIG. 3. (1)...Preamplifier, (2)...Power amplifier, (
3)...detection rectifier circuit, (4) comparator, (5)...
DC amplifier, (9) time constant circuit. Note that the same reference numerals in each figure indicate the same or corresponding parts.

Claims (1)

[Claims] The output of a detection rectifier circuit that detects a DC voltage proportional to the output of a power amplifier is compared with a reference voltage by a comparison circuit, and the output of the power amplifier is feedback-controlled in a direction to make the difference zero. In the automatic output control device, a time constant circuit is configured to compensate for the time response characteristics of the output, the reference voltage is connected to the input point of the time constant circuit, and the output point of the time constant circuit is connected to the reference voltage of the comparison circuit. An automatic output control device characterized by being connected to an input terminal.